需要电子档书籍可以Q群:828202939 希望可以和大家一起学习、一起进步!!纯手打!!
所有的课程源代码在我上传的资源里面,本来想设置开源,好像不行!博客和专栏同步!
如有错别字或有理解不到位的地方,可以留言或者加微信15250969798,在下会及时修改!!!!!
上一节课我们学习了 颜色与纹理中-将非坐标数据传入顶点着色器的另外一种方式--交错组织
这一节课我们将学习 颜色与纹理中-几何图形的装配和光栅化
我们前面的课程了解到顶点着色器是控制的几何图形的位置、尺寸甚至指定几何图形的颜色,最终片元着色器来决定几何图形的颜色!但是我们并不知道他们之间的具体过程!
下面我们来看一下顶点着色器和片元着色器之间的千丝万缕:
需要了解的属性:
顶点着色器到片元着色器的过程:
前面的gl.deawArrays()函数的执行过程(n=3):
示例代码:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>webgl第24课-几何图形的装配和光栅化</title>
</head>
<body onload="main()">
<canvas id="webgl" width="400" height="400">
Please use a browser that supports "canvas"
</canvas>
<script src="../lib/webgl-utils.js"></script>
<script src="../lib/webgl-debug.js"></script>
<script src="../lib/cuon-utils.js"></script>
<script src="../lib/cuon-matrix.js"></script>
<script src="HelloTriangle_FragCoord.js"></script>
</body>
</html>
// HelloTriangle_FragCoord.js (c) 2012 matsuda
// Vertex shader program
var VSHADER_SOURCE =
'attribute vec4 a_Position;\n' +
'void main() {\n' +
' gl_Position = a_Position;\n' +
'}\n';
// Fragment shader program
var FSHADER_SOURCE =
'precision mediump float;\n' +
'uniform float u_Width;\n' +
'uniform float u_Height;\n' +
'void main() {\n' +
' gl_FragColor = vec4(gl_FragCoord.x/u_Width, 0.0, gl_FragCoord.y/u_Height, 1.0);\n' +
'}\n';
function main() {
// Retrieve <canvas> element
var canvas = document.getElementById('webgl');
// Get the rendering context for WebGL
var gl = getWebGLContext(canvas);
if (!gl) {
console.log('Failed to get the rendering context for WebGL');
return;
}
// Initialize shaders
if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {
console.log('Failed to intialize shaders.');
return;
}
// Write the positions of vertices to a vertex shader
var n = initVertexBuffers(gl);
if (n < 0) {
console.log('Failed to set the positions of the vertices');
return;
}
// Specify the color for clearing <canvas>
gl.clearColor(1.0, 1.0, 1.0, 1.0);
// Clear <canvas>
gl.clear(gl.COLOR_BUFFER_BIT);
// Draw the rectangle
gl.drawArrays(gl.TRIANGLES, 0, n);
}
function initVertexBuffers(gl) {
var vertices = new Float32Array([
0, 0.5, -0.5, -0.5, 0.5, -0.5
]);
var n = 3; // The number of vertices
// Create a buffer object
var vertexBuffer = gl.createBuffer();
if (!vertexBuffer) {
console.log('Failed to create the buffer object');
return -1;
}
// Bind the buffer object to target
gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
// Write date into the buffer object
gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);
// Pass the position of a point to a_Position variable
var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
if (a_Position < 0) {
console.log('Failed to get the storage location of a_Position');
return -1;
}
gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0);
var u_Width = gl.getUniformLocation(gl.program, 'u_Width');
if (!u_Width) {
console.log('Failed to get the storage location of u_Width');
return;
}
var u_Height = gl.getUniformLocation(gl.program, 'u_Height');
if (!u_Height) {
console.log('Failed to get the storage location of u_Height');
return;
}
// Pass the width and hight of the <canvas>
gl.uniform1f(u_Width, gl.drawingBufferWidth);
gl.uniform1f(u_Height, gl.drawingBufferHeight);
// Enable the generic vertex attribute array
gl.enableVertexAttribArray(a_Position);
// Unbind the buffer object
gl.bindBuffer(gl.ARRAY_BUFFER, null);
return n;
}
运行展示: